In integrated circuit (IC) devices, magnetic random access memory (MRAM) is an emerging technology for next generation embedded memory devices. MRAM is a memory device including an array of MRAM cells each of which stores a bit of data using resistance values, rather than electronic charge. Each MRAM cell includes a magnetic tunnel junction (MTJ) cell, the resistance of which can be adjusted to represent logic “0” or logic “1.” Conventionally, the MTJ cell includes an anti-ferromagnetic (AFM) pinning layer, a ferromagnetic fixed, or pinned, layer, a thin tunneling barrier layer, and a ferromagnetic free layer. The resistance of the MTJ cell may be adjusted by changing the direction of the magnetic moment of the ferromagnetic free layer with respect to that of the fixed magnetic layer. In particular, when the magnetic moment of the ferromagnetic free layer is parallel to that of the ferromagnetic fixed layer, the resistance of the MTJ cell is low, corresponding to a logic 0, whereas when the magnetic moment of the ferromagnetic free layer is anti-parallel to that of the ferromagnetic fixed layer, the resistance of the MTJ cell is high, corresponding to a logic 1. The MTJ cell is coupled between top and bottom electrodes and an electric current flowing through the MTJ cell from one electrode to the other may be detected to determine the resistance, and therefore the logic state, thereof.
MRAM based on spin transfer torque (STT) switching has been intensively developed as a promising non-volatile RAM. However, because an MTJ cell is composed of one or several thin (i.e., <20 Å) films, reducing interface roughness and enhancing crystal anisotropy are important factors in improving magnetoresistance percentage (MR %) and thermal stability of the MTJ cell. Currently, one technique for smoothing the interface of the MTJ is to adjust the parameters of the MTJ deposition; however, this technique does not result in sufficient smoothness. Moreover, the technique causes degradation of magnetic properties of the MTJ cell, such as MR %, as well as switching field (Hc) and resistive area (RA).
Accordingly, it would be desirable to provide an improved STT-MRAM structure and method of manufacturing thereof absent the disadvantages discussed above.